merge revision(s) f3c77bd480834f2835fe6fef5c0475336248dbde: [Backport #18489]

	Fix the placeholder subclass entry skipping [Bug #18489]

	---
	 class.c                  | 3 +--
	 test/ruby/test_module.rb | 9 +++++++++
	 2 files changed, 10 insertions(+), 2 deletions(-)

1 files changed, 1 insertions, 2 deletions

diff --git a/class.c b/class.c
index 5d3d46d1e6..65a989f9d7 100644
--- a/class.c
+++ b/class.c
@@ -1053,8 +1053,7 @@ rb_include_module(VALUE klass, VALUE module)
     if (RB_TYPE_P(klass, T_MODULE)) {
         rb_subclass_entry_t *iclass = RCLASS_SUBCLASSES(klass);
         // skip the placeholder subclass entry at the head of the list
-        if (iclass && iclass->next) {
-            RUBY_ASSERT(!iclass->klass);
+        if (iclass && !iclass->klass) {
             iclass = iclass->next;
         }